Fuel tanks for motorized vehicles have been in use for many years. In large part, the typical fuel tank currently in use is a generally box-like, cylindrical or rectangular shape and can contain from about 40 to 100 liters or more of a liquid fuel. Fuels can include diesel fuel, gasoline, gasohol, etc. Commonly, a fuel tank can be manufactured by welding, typically metallic half-shell portions to form a sealed tank system. Other metal forming and sealing systems are known. A fuel neck or filler tube is often installed in the tank with a variety of sealing mechanisms. Such a fuel filler tube can be also closed with vapor safe closure or valve mechanisms to prevent the escape of fuel vapor during fueling and use. The current fuel tanks installed in motorized vehicles are typically metallic in nature and are typically quite impermeable to the passage of fuel vapor. Typically, vapor can be lost through joints between metal sections, from an instrument sensor port, from the fuel line leading to the engine, or from the fuel neck during fueling of the vehicle. Examples of fuel containment systems used during fueling are shown in Weissenbach, U.S. Pat. No. 4,131,141; Thompson et al., U.S. Pat. No. 4,977,936; and Johnson et al., U.S. Pat. No. 4,598,741.
Recently, a great deal of attention has been given to improvements in fuel tank design. A large number of patents have been directed to the manufacture of fuel tanks from thermoplastic, composite or thermosetting materials using a variety of laminate or composite structures. Such structures can include layers derived from thermoplastic materials, thermosetting materials, natural and synthetic fibers, metallic fibers, metallic layers, coating layers derived from aqueous and solvent born compositions, etc. One problem arising from the use of such materials in a fuel container relates to the increased permeability of fuel vapor through the organic polymeric container materials when compared to metal tanks. A fuel tank comprising a large proportion of a thermoplastic resin such as polyethylene or polypropylene as a major structural component can have a substantial fuel permeability. Such tanks can release significant proportions of fumes or vapor typically comprising an aromatic, an aliphatic, an oxygenate, an alcohol, etc. or mixtures thereof. Other thermoplastic or thermosetting materials, depending on their chemical constituents, can also release some proportion of the aromatic compound content of fuels, oxygenated materials such as methyl tertiary butyl ether, ethanol, methanol, etc.
Any successful fuel tank using improved technologies must have improved barrier properties to the passage of fuel vapor through the tank. One technique used to improve the barrier properties of fuel tanks involves the formation of a multilayer structure having one or more layers with improved barrier properties. Harr, U.S. Pat. No. 3,616,189 teaches an improved container having multiple layers including a nylon barrier film. Beeson et al., U.S. Pat. No. 5,102,699 teach a film laminate using polyvinyl alcohol as a solvent barrier layer. Delimony et al., U.S. Pat. No. 5,230,935 teach a multilayer material using a variety of compositions to improve the barrier properties of the material. Spurgat, U.S. Pat. No. 5,398,729 teaches a fuel hose having barrier properties derived from layers of impermeable tape, metallic layers which are helically wrapped around a tubular rubber extrusion. These structures have had some success in improving barrier properties. However, the manufacturer of multilayered or laminate materials often involves complex, expensive processing steps and expensive materials.
Specific chemical barrier additive materials have been added to fuel tankage structures to improve barrier properties. Walles, U.S. Pat. No. 3,740,258 and Shefford, U.S. Pat. No. 4,371,574 teach that the addition of sulphonic acid or sulphonate groups on the surface of tank materials can improve barrier properties. These groups are formed by sulfonating the polymer surface with gaseous sulfonation reagents. Gerdes et al., U.S. Pat. No. 4,719,135 teach improving barrier properties of fuel tanks using a varnish coating comprising an epoxy resin, an amine, a curing agent, and a flexibilizer or plasticizer material. Stock, U.S. Pat. No. 4,938,998 teaches that a phosphate, sulfate, carbonate or amino functionalized cellulose derivative as a surface coating, on a polypropylene or polyethylene tank, can improve barrier properties to the passage of fuel vapor. Barton et al., U.S. Pat. No. 4,965,104 teach that closed thermoplastic containers based on copolymers of carbon monoxide or sulfur dioxide can have improved barrier properties. Delcorps et al., U.S. Pat. No. 5,006,377 teach that improved barrier membranes containing a chlorine containing polymer and an adhesive layer consisting of a copolyamide, having a specific degree of crystallization, when combined with a fluorine containing polymer can form improved barrier layers. Hobbs, U.S. Pat. No. 5,244,615 teaches that improved barrier properties to the passage of hydrocarbon fuel vapor can be improved using a fluorinated polymer. In Hobbs, during blow molding of a fuel container, a measured amount of fluorine gas is introduced into the blowing gas. During molding operations, fluorine gas reacts with the polymer composition at the elevated molding temperature to effectively fluorinate the surface resulting in an improved barrier layer. Saito et al., U.S. Pat. No. 5,314,733 teach a multilayer fuel container structure. The multilayer composite comprises a first structural layer, an adhesive layer and a third structural layer.
While many of these systems that involve the use of chemical agents to improve barrier properties have utility in barrier systems, many of these systems involve corrosive chemical systems, complex laminate structures, and other aspects that would require significant investment in developing effective manufacturing methods. Significant need for improvement in fuel vapor barrier systems is present in this fuel tank technology.